Health Department - How Do I Identify a Mouse Problem?

Although these animals are seldom seen because of their nocturnal habits, several signs can be used to identify their presence. The most common signs are rodent droppings, damage to food stuffs, squeaking or rustling sounds in walls or ceilings and evidence of gnawing. House mice also have a characteristic musky odor and may build nests out of finely shredded paper in a sheltered location (behind a refrigerator, washing machine). If you see a mouse in your house or garage, chances are there are several more making your home their home. Act quickly, mice reproduce rapidly.

Mouse versus Rats
A house mouse (Mus musculus) is about 2 to 4 inches long. They weigh between 1/2 - 3/4 of an ounce. They have poor vision but extremely well-developed senses of hearing, taste, and smell. They are primarily seed and grain eaters but are attracted to high protein and sweet foods. They are excellent swimmers and climbers and can jump up 13 inches from the floor. A mouse can squeeze through an opening as small as the diameter of a pencil. Mice may spend their entire life span within a 25 foot range. They are not reliant upon water as they extract moisture from their food.

Rats (Rattus norvegicus) are large, about 6 to 12 inches long (excluding the 7-7 1/2" tail). They usually weigh between 10-17 ounces. Like the house mouse, they have poor vision but a highly developed senses of taste, smell and hearing. They can jump 3 feet or more from a standing start. Rats are burrowing animals and generally live underground. Burrows are generally 8 to 18 inches below the surface. A rat's front teeth grow approximately 5 inches a year. Therefore, a rat must gnaw to live. If the teeth are not worn down through gnawing, the rat will die of starvation. Rats have been known to gnaw through lead pipes and poorly-mixed concrete. Rats need water and will start their evening searching for a water source.

What Dangers Should I be Aware of?
Rats and mice can transmit several diseases including salmonellosis, plague and typhoid. They also contaminate food, damage structures, and carry parasites (fleas, mites, tapeworms and pinworms) and can aggravate asthma. In addition, these rodents can cause fires and/or short out equipment by gnawing on electrical wiring.

Why do Mice Become a House Problem?
There are several reasons. Mice are attracted to food and comfortable shelter just as we are. As cold weather approaches they seek warm shelter. They will feed on a variety of foods including pet food, fruit, sweets, birdseed and, of course garbage. They can live under porch and patio concrete slabs, utility sheds, wood piles and compost heaps.

While mice commonly live outside, they may seek shelter indoors. They enter through small openings (1/4 inch) around pipes and conduits in walls and floors, broken screens and vents, or poorly fitting doors. Once inside, a female may have 5-10 litters of 5-6 young every year. The life span of a mouse is generally nine to twelve months.

How Can I Prevent a Rodent-Problem?
Store garbage, recyclable materials, dry pet food and birdseed in rodent proof containers.  Clean up outside trash and debris. Use raised concrete foundations under sheds and woodpiles.  The foundation should be at least12 inches above the ground to discourage gnawing and 24 inches into the ground to discourage burrowing. Cut grass and dense shrubbery around the perimeter of your house. Seal possible rodent entry ways, and trim overgrown weedy areas.

Check openings around pipes. Where pipes enter a wood wall, fit sheet metal (24 gauge or heavier) around the pipe. Where pipes enter masonry, force hardware cloth (24 gauge) into the opening around the pipe and fill with cement. Seal around basement windows and doors. 22 gauge aluminum or heavier should be used for frames and flashings.

Mice are good swimmers so it is possible for them to enter homes through a house drain. Keep floor drains tightly fastened to prevent entry into your home.

A mouse's upper teeth curve inward so it is difficult for them to gnaw into flat hard surfaces. To find a way into your home mice search for chipped or indented corners to gnaw. Sealing material should be smooth on the outside to prevent mice from pulling out or chewing through the compound. Plastic sheeting, screen, wood and rubber are not suitable for sealing rodent entry ways.

What do I do if I Detect a Rodent Problem?
One or two mice can often be controlled by the homeowner with glueboards, mechanical traps and/or rodent baits. When positioning traps, keep in mind that house mice rarely stray more than 25 feet away from their nest. Bait should be placed 10-15 feet apart, along the walls where the mice travel. Areas where the rodent has run should be disinfected with a household disinfection agent. All food sources should be sealed in rodent-proof containers.

One cannot rely on their pet to eliminate a rodent problem. Dogs and cats often live peacefully with rodents. In fact, mice and rats often live off of food from pet dishes. In addition, there is very little evidence that sound or electronic devices will drive rodents from their shelter.

Please note: If you see one mouse it is very likely there are several members of their family hiding nearby. Rats or large mouse populations are difficult to control. You may need to call a professional pest control operator.

About this Guide
This brochure is a public resource guide that is available from the Skokie Health Department and from the Public information Division. For additional information on the Health Department's many programs and services please visit the Village of Skokie web site at www.skokie.org .

Final Notes
The Skokie Health Department is pleased to answer your questions. Please contact the Health Department at (847) 933-8252 if you need assistance.